Ink roller for printing machine

ABSTRACT

According to a printing machine ink roller and a method of the invention for manufacturing the same, a surface layer (18) consisting of a synthetic resin or a rubber-like material, which has ink absorbency and which allows surface polishing, is arranged on a surface of a mandrel, a large number of substantially spherical particles are mixed in the surface layer (18), and a large number of independent projections (16) are formed by partially exposing predetermined substantial particles in a surface region (17) of the surface layer (18). The ink roller can maintain a function of transferring a predetermined amount of ink for a long period of time so that the performance of a printing machine can thus be improved, and such a printing machine can be very easily manufactured and repaired.

TECHNICAL FIELD

The present invention relates to an ink roller for a printing machine,which is used as an ink metering roller in an inking unit of a printingmachine such as a flexographic printing machine, an offset printingmachine, and a relief printing machine, and a method of manufacturingthe same.

BACKGROUND ART

A roller called an anilox roller is used as an ink metering roller in aninking unit. The anilox roller has a function of supplying and meteringink. The function is realized by a plurality of independent recesses(cells) 1a and 2a formed by a laser or mechanical processing on outersurfaces 1 and 2 of the roller composed of a metal or ceramic, as shownin FIGS. 1 and 2.

FIG. 3 shows a schematic arrangement of a flexographic printing machine.Ink 4 in ink pan 3 is transferred onto plate cylinder 6 by anilox roller5. In this case, excess ink 4 is scraped off by doctor blade 7 incontact with anilox roller 5. Doctor blade 7 is made of steel, a resin,or the like. Only a necessary amount of ink 4 is transferred onto platecylinder 6 while it is filled in the recesses formed on the outersurface of the anilox roller. An ink film is transferred from platecylinder 6 to printing material 9 such as paper urged against platecylinder 6 by the pressure of impression cylinder 8, thereby performingpredetermined printing.

FIG. 4 shows a schematic arrangement of a keyless offset printingmachine. In this case, ink 4 in ink pans 3 is transferred from fountainrollers 10 to anilox rollers 5. Ink 3 is transferred therefrom to inkforme rollers 11 made of rubber, and then is transferred onto platecylinders 6. In this case, excess ink 3 is also scraped off by doctorblades 7 brought into contact with anilox rollers 5. Subsequently, inkfilms are transferred from plate cylinders 6 to rubber blanket cylinders12 in contact with plate cylinders 6. The ink films are transferred fromrubber blanket cylinders 12 to printing material 9 so as to performpredetermined printing.

Dampening water units 13 serve to form non-image area. Morespecifically, dampening water units 13 supply dampening water 15 usingdampening rollers 14 onto the non-image area before ink is supplied tothe plate cylinders, thereby preventing adhesion of the ink to nonimagearea.

Accordingly, the ink transfer ability of anilox roller 5 having a largenumber of recesses formed on its outer surface greatly influencesprinting quality. According to a method of forming recesses on such ananilox roller, for example, a mother mold is urged against the outersurface of a mandrel such that recesses are sequentially formed from oneend portion of the mandrel. Then, in order to provide wear resistance tothe roller, the outer surface of the mandrel is plated with copper orchromium. According to another method, as described above, a ceramic isflame-sprayed on a mandrel and is grinded, and then recesses areengraved by a laser. Quadrangular pyramid-shaped or quadrangularfrustrum pyramid-shaped recesses are often employed. In addition, thenumber of recesses is set to correspond to the number of lines formed onthe outer surface of a mandrel at a rate of, e.g., 165 lines/inch, 180lines/inch, or 200 lines/inch. The depth of each recess and the amountof ink to be transferred by an anilox roller are decreased with anincrease in number of recesses. According to specific requirements ofsuch recesses (cells), 1 high shape precision must be attained, and 2ink is not easily peeled off by dampening water from anilox roller (inoffset printing).

The following drawbacks are posed in a conventional anilox roller.

(1) Anilox rollers having recesses formed by a mother die

1 The shapes of recesses vary widely on a roller or between rollers.

2 The outer surface of a roller is worn out by a doctor blade, and theshapes of the recesses change upon use of the roller. Consequently, theink storage amount of the recesses is gradually decreased and thedensity of a printing matter is changed.

3 In an arrangement wherein recesses are independent from each other,ink is rejected because of excessive dampening water, i.e., a strippingphenomenon is caused. Note that a normal depth of each recess is 15 to14 μm.

(2) Anilox rollers having recesses formed by a laser

1 Large-scale facilities are required to form recesses and rollers.

2 If the outer surface of a roller is damaged, it cannot be repaired.Therefore, a new roller must be manufactured.

3 Heat is generated between a doctor blade and an anilox roller becauseof friction. For this reason, a rubber roller in contact with the aniloxroller is expanded. As a result, the nip width of the rubber roller mustbe adjusted.

4 A stripping phenomenon is caused because of excessive dampening water.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide an ink roller for aprinting machine, which can maintain the metering function of apredetermined amount of ink for a long period of time, and improve theprinting performance of the printing machine, and which can be veryeasily manufactured and repaired, and a method of manufacturing thesame.

More specifically, according to the presentinvention, an ink roller fora printing machine is characterized by comprising a mandrel, a surfacelayer consisting of a synthetic resin or a rubber-like material, whichis formed on a surface of the mandrel, has ink absorb, and allowssurface polishing, a large number of substantially spherical particlesmixed in the surface layer, and a large number of independentprojections formed by the large number of substantially sphericalparticles partially exposed on a surface region of the surface layer.

In this case, it is preferable to use any one of urethane, polyamide,epoxy, polyvinyl chloride, polyester, phenolic, urea, polyimide, andpolyamide-imide resins as the synthetic resin. In order to adjust inkabsorb of the surface layer, two or more of these resins havingdifferent ink affinities may be used as needed.

In addition, it is preferable to use any one of nitrile rubber, urethanerubber, chloroprene rubber, acryl rubber, epichlorohydrin rubber,chlorosulfonated polyethylene, chlorinated polyethylene, fluororubber,ethylene propylene rubber, polybutadiene rubber, and natural rubber asthe rubber-like material. In order to adjust ink absorb of the surfacelayer, two or more of these rubbers having different ink affinities maybe used.

Each of the synthetic resin and the rubber-like material has slight inkpermeability. This ink permeability increases the ink affinity of thesurface layer. As a result, a desired ink absorb of the surface layer isrealized. Therefore, when the ink roller for the printing machine isused, frequency of occurrence of troubles such as stripping is greatlyreduced even if excessive dampening water is supplied, thereby assuringstable printing. Note that when the synthetic resin and rubber-likematerial of the types described above are observed by a microscope afterthey are used as a rubber roller for, e.g., one year, ink permeabilityof about 1 mm is confirmed. Predetermined types of synthetic resins andrubber-like materials should be determined in accordance with the typeof ink to be used. It is not preferable to use one having excessivepermeability because the external shape of the surface layer is changed.

A copper powder or a copper alloy such as brass or bronze may be mixedin the surface layer to realize a predetermined ink affinity or toadjust it. The hardness of the surface layer is preferably set to be 80or more in Shore hardness A. This is because the surface layer isgreatly worn out by the doctor blade if the hardness is less than 80.

The substantially spherical particles preferably consist of any one ormore of silica, alumina (Al₂ O₃), aluminosilicano, ceramic, glass,stainless steel, epoxy resin, and phenolic resin spherical particles. Itis preferable to determine which of these particles is used inconsideration of differences in polishing property and affinity with thesynthetic resin or the rubber-like material described above. In general,substantially spherical particles of silica or alumina manufactured byhigh-temperature flame spraying are preferably used.

Each particle is required to have a substantially spherical shape forthe following reasons.

It is because the substantially spherical shape can prevent the printingmachine ink roller from being damaged by the doctor blade in contacttherewith and also prevent abrasion of the doctor blade itself. Ifalundum or corundum particles of irregular shapes are used instead ofspherical particles, the surface of the roller is damaged, and otherrollers may be damaged. By using spherical particles, heat generatedwhen the ink roller is brought into contact with other rollers can besuppressed. In addition, if spherical particles are used, excellent flowor fill characteristics can be obtained, thereby facilitating themanufacture of the printing machine ink roller.

The substantially spherical particles are made harder than the syntheticresin and the rubber-like material for the following reasons. With thisarrangement, projections can be easily formed to be independent fromeach other only by grinding surface layer 18, harder particles stay onthe roller surface keeping the shape without abrasion, to form exposingprojections. As a result, an ink storage section can be formedthroughout the even regions between projections 16 and surface layer 18.In addition, by forming hard substantially spherical particles, theshape of the ink storage section can be maintained with high precisionfor a long period of time, thereby maintaining excellent transferperformance of ink. For this reason, in case of the keyless offsetprinting machine shown in FIG. 4, this printing machine ink roller isused instead of anilox roller 5. In this case, ink 4 in an ink storagesection (corresponding to the portion denoted by reference numeral 17 inFIG. 5) of ink roller for printing machine's surface 18 is transferredonto forme roller 11. Transfer of ink 4 is performed at a position wherethe nips of ink roller for printing machine's surface 5 and forme roller11 are separated from each other. Since ink 4 in ink storage section 17is continuous, a so-called vacuum effect caused in conventional aniloxroller 1a, 1b shown in FIG. 1, FIG. 2 can be prevented. As a result,transfer of ink 4 can be extremely effectively and easily performed. Inaddition, the present invention is advantageous in that even when thesurface of a roller is accidentally damaged or worn out, a new surfacelayer having a large number of independent projections can be formed bysimply polishing the surface of the roller again using a whetstone orthe like.

Each of the substantially spherical particles is preferably formed intoa spherical shape within the range of 5 to 100 μm, more preferably therange of 10 to 60 μm when the thickness of an ink film required for inktransfer is taken into consideration.

The thickness of an ink film or the density of ink in printing usingthis printing machine ink roller is determined by setting the amount andsize of the substantially spherical particle to be predetermined values,respectively. For example, when the density of ink is decreased bythinning an ink film, small substantially spherical particles are usedto reduce the gap between the doctor blade in contact with the printingmachine ink roller. In contrast to this, when the density of ink isincreased by thickening an ink film, large substantially sphericalparticles are used to increase the gap between the printing machine inkroller and the doctor blade.

Furthermore, according to the present invention, there is provided amethod of manufacturing a printing machine ink roller, in which asurface layer having a large number of recesses and projections formedin a surface region is formed on an outer surface of a mandrel,characterized in that a surface layer is formed by the steps of mixing amatrix consisting of a synthetic resin or a rubber-like material havingink absorbency with a large number of substantially spherical particleshaving a hardness higher than that of the matrix, forming the matrix andthe substantially spherical particles integrally with each other bycuring or crosslinking the mixture obtained in the preceding step so asto form a surface layer material, and partially exposing arbitraryparticles of the large number of substantially spherical particles bypolishing the surface layer material so as to form a large number ofindependent projections.

A cast molding method, a rotational molding method, a sheet windingmethod, a reaction injection molding (RIM) method, or a flame sprayingmethod can be used as a means for causing the surface layer to beadhered to the mandrel.

The cast molding method can be used when the matrix has a liquid form.In this method, a matrix, substantially spherical particles, and acuring agent are mixed, and then the resultant mixture is degassed toform a mixture for forming a surface layer. Subsequently, a mandrelhaving an adhesive coated on its surface is set in a mold. The mixtureis poured into the mold and cured to form a surface layer integratedwith the mandrel. After this, the surface layer is polished to form aprinting machine ink roller.

In the rotational molding method, a cylindrical mold for rotationalmolding is prepared. Then, the inner surface of a cavity portion of themold is polished and a mold lubricant is coated on the inner surface. Amixture obtained in the same manner as that in the cast molding methodis poured into the cavity. The mixture is subjected to rotationalmolding at a predetermined temperature for a predetermined period oftime and is cured to form a portion corresponding to a surface layer.The resultant surface layer is released from the mold and its innersurface is grinded. Then, a predetermined mandrel is fitted into thesurface layer by, e.g., shrink fitting. The surface layer is polished toform a printing machine ink roller.

The sheet winding method can be used when a matrix has a solid form andis of a kneading type. In this method, substantially sphericalparticles, a crosslinking agent, and other necessary chemicals such as aprocessing aid are mixed with the matrix using milling rolls to form asheet. Then, the sheet is wound around a predetermined mandrel. Thewound sheet is subjected to a heat treatment to form a surface layerintegrated with the mandrel. Subsequently, the surface layer issubjected to a polishing treatment to obtain a printing machine inkroller. In this case, the surface layer to be wound around the mandrelmay be formed by extrusion molding.

In these method, polishing is performed by a whetstone or an abrasivecloth.

In addition, the types of a synthetic resin, a rubber-like material, andthe substantially spherical particles, and the shape of thesubstantially spherical particle are the same as those in theabove-described methods.

The content of the substantially spherical particles to be mixed withthe matrix is 10 to 400 parts by weight with respect to 100 parts byweight of the matrix. If the content is less than 10 parts by weight, alevel difference for forming an ink storage section becomesinsufficient. If the content exceeds 400 parts by weight, the number ofprojections becomes too large, thereby degrading ink retainingperformance.

Moreover, a copper powder or a copper alloy such as brass or bronze maybe mixed with the matrix as needed. In this case, the amount of copperpowder to be mixed with the matrix is preferably 50 to 400 parts byweight with respect to 100 parts by weight of the matrix.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A)-(B) and 2(A)-(B) are views illustrating recesses formed inthe outer surfaces of anilox rollers;

FIG. 3 is a view illustrating a schematic arrangement of a flexographicprinting machine;

FIG. 4 is a view illustrating a schematic arrangement of a keylessoffset printing machine; and

FIG. 5 is a perspective view showing a surface layer of a ink rolleraccording to an embodiment of the present invention.

THE BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below.

EXAMPLE 1

100 parts by weight of Sannix HR-450P (polyol available from SANYOCHEMICAL INDUSTRIES, LTD.) were heated/dehydrated, and 150 parts byweight of hard spherical particles S-COL (available from MICRON Co.,Ltd.) consisting of silica having an average grain size of 25 μm weremixed therewith. Then, 110 parts by weight of Millionate MT (isocyanateavailable from Nihon Polyurethane Co., Ltd.) were added to the resultantmixture, and the mixture was agitated at a reduced pressure to obtain amaterial for forming a surface layer.

After having treated a mandrel so as to remove any rust or greasetherefrom, an adhesive was coated on the mandrel and the mandrel wasthen placed in a mold. Then, the material obtained in theabove-described manner was poured into this mold and heated at 85° C.for six hours to be cured, thereby forming a surface layer on thesurface of the mandrel. Subsequently, the molded product was releasedfrom the mold and sufficiently cooled, and the surface layer wassurface-polished using a whetstone to form a surface layer having anouter diameter of 175 mm and a thickness of 5 mm.

A printing machine ink roller obtained in this manner had a surfaceroughness (Rz) of 5 to 7 μm and a Shore D hardness of 87. This printingmachine ink roller was mounted on the same printing machine as shown inFIG. 4 as anilox roller 5, and printing was performed at 300 rpm for sixhours. In this case, since no variation in ink density occurred, anexcellent printed matter can be said to have been obtained. When thesolid density of this printed matter was measured by a GRETAGdensitometer D142-3, a density of 0.9 was recorded.

EXAMPLE 2

100 parts by weight of anhydrous ε-caprolactam were heated to 80° C.,and then 0.5 mol % of metal potassium was added and mixed therewith. 30parts by weight of hard spherical particles CB-A40 (available from ShowaDenko Co., Ltd.) consisting of alumina having an average grain size of42 μm were mixed with the resultant mixture. Subsequently, 0.5 mol % oftolylene diisocyanate was added to this mixture and heated to 120° C. toobtain a material for forming a surface layer.

This material was poured in a mold for rotational molding and wasrotated at 750 rpm at 145° C. to be cured, thereby forming a surfacelayer having an outer diameter of 176 mm. Then, an iron core wasshrink-fitted in this surface layer. The surface layer was polished by awhetstone to form a surface layer having an outer diameter of 175 mm anda thickness of 5 mm.

A printing machine ink roller obtained in this manner had a surfaceroughness (Rz) of 10 to 15 μm and a Shore D hardness of 80. Thisprinting machine ink roller was mounted onto a keyless offset printingmachine as an ink metering roller, and printing was performed at 300 rpmfor five hours. In this case, since no variation in ink densityoccurred, an excellent printed matter can be said to have been obtained.When the solid density of this printed material was measured by a GRETAGdensitometer D142-3, a density of 1.05 was recorded.

EXAMPLE 3

10 parts by weight of HY956 (available from Nihon Chiba Gaigy Co., Ltd.)serving as a curing agent were mixed with 100 parts by weight of epoxyresin Araldite AY101 (available from Nihon Chiba Gaigy Co., Ltd.). Then,200 parts by weight of hard spherical particles of Alunabeads CB-A50(available from Showa Denko Co., Ltd.) consisting of alumina having anaverage grain size of 50 μm were mixed with the resultant mixture. Thismixture was agitated and degassed to obtain a material for forming asurface layer.

After derusting and degreasing treatments, an adhesive was coated on amandrel and the mandrel was set in a mold. The material obtained in theabove-described manner was poured in the mold and was left to stand in aroom, in which a temperature was controlled to be about 40° C., for 24hours to be cured, thereby forming a surface layer on the surface of themandrel. After this was released from the mold, the surface layer waspolished by a whetstone to obtain a printing machine ink roller havingan outer diameter of 175 mm and a thickness of 5 mm.

The printing machine ink roller obtained in this manner had a surfaceroughness (Rz) of 13 to 15 μm, and a Shore D hardness of 85. Thisprinting machine ink roller was mounted on a keyless offset printingmachine, and continuous printing was performed at 300 rpm for eighthours per day for six months. In this case, a uniform printed matter wasobtained without causing stripping. When the solid density of thisprinted matter was measured by a GRETAG densitometer D142-3, 1.1 wasrecorded.

EXAMPLE 4

100 parts by weight of a copper powder Cu-At-W-250 (available fromFukuda Kinzokuhakufun Co., Ltd.) and 180 parts by weight of hardspherical particles of Alunabeads CB-A60 (Showa Denko Co., Ltd.)consisting of alumina having an average grain size of 60 μm were mixedwith 100 parts by weight of PolybdR45HD (polybutadiene available fromIdemitsu Sekiyu Kagaku Co., Ltd.). This mixture was agitated anddegassed. Then, 15 parts by weight of Isonate 143L (available from KaseiUpjohn Co., Ltd.) serving as a curing agent and 0.01 parts by weight ofcatalytic dibutyl tin dilaurate were added to the mixture and weresufficiently mixed together to obtain a material for forming a surfacelayer.

After derusting and degreasing treatments, an adhesive was coated on amandrel and the mandrel was set in a mold. This material was poured inthe mold and was left to stand at room temperature for three days to becured, the surface layer was polished by a whetstone, thereby forming asurface layer having an outer diameter of 175 mm and a thickness of 5mm.

A printing machine roller obtained in this manner had a surfaceroughness (Rz) of 15 to 17 μm and a Shore A hardness of 80. Thisprinting machine ink roller was mounted on a flexographic printingmachine, and printing was performed at a speed of 100 m/min. In thiscase, no variation in printing was found. When the solid density wasmeasured by a GRETAG densitometer D142-3, 1.2 was recorded.

EXAMPLE 5

    ______________________________________                                        Composition                                                                                        Parts by                                                                      weight                                                   ______________________________________                                        JSRN230 (nitrile rubber available                                                                    100                                                    from Nihon Goseigomu Co., Ltd.)                                               zinc oxide              5                                                     sulfur                 40                                                     accelerator D           2                                                     stearic acid            1                                                     clay                   50                                                     Sumilight resin PR310 B (a phenolic                                                                  30                                                     resin available from Sumitomo                                                 Jurettsu Co., Ltd.)                                                           Nipole (liquid nitrile rubber                                                                        10                                                     available from Nihon Zeon Co., Ltd.)                                          Alunabeads CB-A30 (hard spherical                                                                    150                                                    alunabeads having an average                                                  grain size of 30 μm available                                              from Showa Denko Co., Ltd.)                                                   ______________________________________                                    

The above-described composition was sufficiently kneaded by millingroll. Then, the resultant composition was formed into a sheet having athickness of about 2 mm using calender roll. A separately mandrel wassandblasted. Subsequently, rubber cement prepared by dissolving thecomposition into toluol was coated on the surface of the mandrel. Thesheet prepared in the above-described manner was wound around themandrel coated with the rubber cement until the thickness of sheetbecame about 8 mm. A cotton tape and a steel wire were wound around theouter surface of the surface layer formed upon winding of the sheet. Inthis state, the resultant product was introduced into a vulcanizer andheated at a water vapor pressure of 4 kg/cm² for eight hours. Thesurface layer vulcanized in this manner was polished by a whetstone and360-mesh sandpaper.

A surface layer having an outer diameter of 175 mm and a thickness of 5mm was formed in this manner. This surface layer had a Shore D hardnessof 90 and a surface roughness (Rz) of 7 to 9 μm.

A printing machine ink roller obtained in this manner was mounted on akeyless relief printing machine, and printing was performed at 3,00 rpmfor four hours. No problem was posed in printing. When the solid densityof a printed matter was measured by a GRETAG densitometer D142-3, 0.95was recorded.

INDUSTRIAL APPLICAPABILITY

The roller of the present invention can maintain a function oftransferring a predetermined amount of ink for a long period of time andcan improve the printing performance of a printing machine, can be veryeasily manufactured and repaired, and can be effectively used as an inktransfer roller in printing machines such as flexographic, offset, andrelief printing machines.

We claim:
 1. An ink metering roller for use in a printing machinecomprising a mandrel, an exterior surface layer formed on said mandrelconsisting of an ink absorbent matrix material of synthetic resin orrubber and having substantially spherical particles mixed therein, saidparticles arranged to form independent, partially exposed projections ona surface region of said surface layer, said particles selected from thegroup consisting of silica, alumina, aluminosilicano, ceramic, glass,stainless steel, epoxy resin, and phenolic resin spherical particles;wherein each of said substantially spherical particles has a grain sizeof from about 5 to 100 μm; and wherein said substantially sphericalparticles are embedded in said surface layer to a depth of at least 2.5μm from said surface region.
 2. An ink metering roller according toclaim 1 wherein said substantially spherical particles have a hardnessgreater than said matrix material, so that said matrix material can beground from said substantially spherical particles to thereby form saidindependent, partially exposed projections.
 3. An ink metering rolleraccording to claim 2 wherein said substantially spherical particlescomprise 10 to 400 parts by weight to 100 parts by weight of said matrixmaterial.
 4. An ink metering roller according to claim 3 having asurface roughness (Rz) of from about 5 to 17 μm and a Shore D hardnessof from about 80 to 87.